A so-called “multi-element” eddy current probe is known that is associated with an imaging system, the probe being specially shaped to slide along a tangential recess in a rotor disk. The rectilinear probe is of constant section; its cross-section has an outline that corresponds to the section of the recess for inspection. It contains a plurality of eddy current sensors arranged for quasi-simultaneous acquisition of a plurality of data series during a scanning stroke in the longitudinal direction of the recess. Each data series corresponds to scanning a longitudinal strip of the inside surface of the recess by means of a single sensor. The probe is moved manually.
The reliability and the accuracy of the measurement depend on the probe being properly positioned in the recess. That is why the sensors are grouped together in a central segment of the probe, between two guide segments that do not have sensors. This ensures that the probe is properly positioned, even at the ends of the recess when the sensors begin to scan the surface state of the recess.
Although associating such a multi-element probe with an imaging system is advantageous, the performance of the system is limited by the presence of the guide segments, i.e. by the impossibility of placing the sensors at the end of the probe. As a result, inspection is not genuinely reliable, unless the central segment of the probe is caused to slide over the entire length of the recess. That can be done on a disk that has been completely dismantled so that the probe can be inserted via one end of the recess and extracted from the other. However, if it is necessary to inspect a rotor made up of a plurality of disks positioned side by side (welded together), then such movement is not always possible.